Scanning antennas using dielectric with variable refraction



H. IAMS Nov. 8, 1960 SCANNING ANTENNAS USING DIELECTRIC WITH VARIABLE REFRACTION Filed March 16, 1948 15 con/max.

VOLMGE SOURCE Inventor.- fiarleylams 1 y If A TTOR/VE Y ited St SCANNING ANTENNAS USING DIELECTRIC WITH VARIABLE REFRACTION Filed Mar. 16, 1948, Ser. No. 15,132

3 Claims. (Cl. 343-754) This invention relates to scanning antenna systems and more particularly to those of the type which produce a relatively narrow directive beam which is periodically displaced through a certain'angle.

The principal object of the invention is to provide improved methods and means for scanning which require no moving parts or complex electrical networks.

More specifically, it is an object of the present invention to vary the position of the beam formed by a directive antenna by varying the dielectric constant of one or more bodies of insulating material incorporated in the antenna structure.

The invention will be described with reference to the accompanying drawing, wherein Figure l is a pictorial view of one embodiment of the invention as applied to an antenna of the leaky wave guide type, and Figure 2 is a modification wherein the propagation velocities in transmission line sections are varied to produce scanning. J The antenna shown in Figure 1 includes a hollow wave guide 1 provided with a plurality of apertures 3, spaced at intervals longitudinally along one side of the guide. One end 5 of the guide 1 is coupled to a utilization device such as a radio transmitter or receiver, not shown. A wedge shaped prism 7 of dielectric material is disposed in front of the openings 3 substantially as shown. Conductive films or plates 9 and 11 are provided on the upper and lower surface respectively of the prism 7, and are connected to respective terminals of a source 13 of control voltage.

To direct the radio frequency energy from the wave guide 1 into the prism 7 additional metal cover plates not shown may be used. These are applied over electrode 9 and under electrode 11 but are insulated therefrom by thin sheets of a dielectric such as mica. The sheets extend from electrodes 9 and 11 to the upper and lower surfaces of the wave guide, thereby providing a structure directing the energy into the prism.

The material of the prism 7 is one having a dielectric constant which varies according to variation in the intensity of an electric field to which the material is subjected. One suitable substance is barium titanate, BaTiO A mixture of barium and strontium titanates may be used, and at present the preferred composition comprises, by Weight, about 70 percent barium titanate and 30 percent strontium titanate. The conductive members 9 and 11 may be thin films of silver, baked into the surface of the prism 7.

In the operation of the system of Figure 1 for transmission, radio energy applied to the end 5 of the guide 1 propagates along the guide. A certain amount escapes from each orifice 3 and is radiated. The effect is substantially that of a linear array of antennas excited in relative phases which depend upon the aperture spacing in terms of the wavelength of the energy in the guide. As a practical matter, the structure can be designed so that all the apertures radiate in phase; for the sake of r 2,95%,733 Patented Nov. 8, 1966 from the guide 1 is deflected by the prism 7, substantially in the same manner as a transparent prism will deflect a beam of light. The amount of deflection depends upon the shape of the prism and the refractive index of the material of which it is made. The refractive index of a dielectric material is the square root of its dielectric constant.

The amount of refraction provided by the prism 7, and hence the direction of the radio beam, is a function of the voltage output of the source 13. For periodic scanning, the source 13 may be an oscillator or alternator. To obtain constant scanning speed, i.e. a certain number of degrees deflection per second, the source. 13 may be designed to produce an output of sawtooth wave form. If the sawtooth is unsymmetrical, with relatively slow build-up and rapid decay, for example, the beam will sweep relatively slowly from one side to the other, and return quickly to its starting point. It will be apparent that scanning in accordance with any particular law may be produced by designing the source 13 to give the required wave shape, or non-repetitive scanning can. be provided by corresponding control of the voltage of the source.

The operation has been described in terms of transmission; however, the structure Will operate similarly for reception, the direction of maximum response being a function of the voltage applied between the plates 9 and 11.

Variation in dielectric constant of a medium may be applied to the control of direction of a radio beam in many other ways than that shown in Figure 1; one example is shown in Figure 2. The antenna in this case includes a linear array of spaced doublets 15, 17 and 19, connected by transmission line sections 2.1, 23 and 25 respectively to spaced points along a transmission line 27. One end 6 of the line 27 is coupled through a capacitor 29 to a utilization device such as a transmitter or receiver. The other end of the line 27, not shown, may terminate in an impedance matching device designed in accordance with principles well known to those skilled in the art.

Bodies 31, 33 and 35 of variable dielectric material, like the above-described titanates, are included in the line sections 21, 23 and 25 respectively. The thickness or extent of each dielectric body along the respective line section may be proportional to the distance of that line section firom the end 6 of the main transmission line 27. The control voltage source 13 is connected between the conductors of the line 27. A choke 37 is included to prevent the flow of radio frequency energy through the source 13.

The shape and orientation of the directive pattern of the system of Figure 4 depends upon the spacing of the elements 15, 17 and 19, and the phase relationships between said elements as viewed from a reference point in the system such as the end 6 of the line 27. Each of the dielectric bodies 31, 33 and 35 introduces a certain amount of phase delay in its respective line section. Suppose that the various line lengths are selected so that, when the variable dielectric material has an intermediate value of dielectric constant, the radiation from the radiators 15, 17 and 19 is in phase. This will result in a directive beam perpendicular to the longitudinal axis of the line 27 Now if the dielectric constant of the material of the bodies 31, 33 and 35 is increased, the phase delay produced by each body will be increased accordingly. The body 31, being the shortest, will produce the least total increase in phase delay; the longer body 33 will provide a proportionately greater phase delay, andso on. As a result, the radiators 15, 17 and 19 will no longer be in phase, but in increasingly retarded phase progressing down the line 27 away from the end 6; The etfect is to displace the axis of the directive pattern through a certain angle in the direction of increasing lag.

Conversely, a decrease in the dielectric constant of the bodies 31, 33 and 35 will deflect the beam toward the end 6 of the line 27. Thus variation of the control voltage from the source 13 will cause corresponding variation in the direction of the beam, substantially as in the system of Figure 1.

The invention has been described as an improvement in directive antennas, wherein scanning or displacement of the directive axis is obtained by variation of the dielectric constant of insulating material through which radio frequency energy is transmitted. Said variation is induced by application of an electric field in addition to or other than that associated with the transmitted energy to the dielectric material, thus enabling scanning without the use of moving parts.

I claim as my invention:

1. A scanning antenna system including an array of radiator means providing a wave front, means including bodies of dielectric material through which the energy of said wave front is transmitted to the respective radiators of said array, the thickness of said bodies being progressively greater from one side of said array to the other, and control means applying a variable electric field other than that associated with said wave front to said bodies to vary the propagation velocity of said energy therethrough and thus vary the phase relationships between said radiators.

2. In an antenna system including means providing a wave front, means including dielectric material composed at least in part of barium titanates through which the energy of said wave front is transmitted, the thickness of said material in the'general direction of transmission of said energy being progressively greater from one part of said wave front to another, and means applying an electric field to said material in addition to that of said energy of said Wave front.

3. An antenna system including a linear array of spaced radiator means phased to provide a substantially linear wave front, means including bodies of dielectric material through which the energy forming said Wave front is transmitted, the thickness of said material in the direction of transmission of said energy therethrough being progressively greater from one end of said array to the other, and control means applying a variable electric field in addition to that associated with said Wave front to said material to vary the propagation velocity of said energy therethrough and thus vary the direction of motion of said wave front.

References Cited in the file of this patent UNITED STATES PATENTS 2,071,564 Nicolson Feb. 23, 1937 2,085,406 Zworykin June 29, 1937 2,129,712 Southworth Sept. 13, 1938 2,142,648 Linder Jan. 3, 1939 2,182,377 Guanella Dec. 5, 1939. 2,411,872 Feldman et al. Dec. 3, 1946 2,415,352 Iams Feb. 4, 1947 2,429,601 Biskeborn et al. Oct. 28, 1947 2,454,530 Tiley Nov. 23, 1948 2,464,276 Varian Mar. 15, 1949 OTHER REFERENCES Industrial and Engineering Chemistry, vol. 38 #11, November 1946, pages 1097 to 1109. 

